Improving Boone powerless to stop Justin Smith’s power move

Alex Boone believes he’s solidified a spot as the Niners’ backup offensive tackle — a move up after lingering on the practice squad as a rookie and being inactive for 15 games last year.

Boone credits part of his improvement to lining up regularly against San Francisco’s defensive linemen, most notably Justin Smith, a two-time Pro Bowler with a one-of-a-kind move: The chop-to-bull.

Never heard of it? Boone explained, in an awed tone, the 6-foot-4, 285-pound Smith’s patented power move.

“The chop to bull is when he chops your arm and then he throws his shoulder into you,” Boone said. “So you shoot your hands, he’ll chop your hands, you tend to lean forward and then he bulls you backward.

“If you watch the film, he gets everybody on it. It’s pretty impressive. You know it’s coming but he still gets you on it somehow. I mean, it’s unbelievable.”

Boone (6-8, 300) has held up well enough against the likes of Smith and rookie Aldon Smith in training camp to cement a roster spot. He took a few first-team snaps at right tackle in place of Anthony Davis on Monday, but offensive coordinator Greg Roman indicated such a move was an example of “contingency planning.” That is, making sure Boone feels comfortable on the right side in case of an injury.

Boone, who has played on the left side during camp, said he initially felt awkward — his muscle memory was messed up — but feels comfortable at both tackle positions.

Boone said he’s working to earn a starting spot, but he’s not there yet.

“I would like to (be),” he said. “But obviously I’ve got to take great strides to get there. Just keep working. Just keep practicing … At the end of the camp, I guess you would hope to be among the best five (offensive linemen).”

* Running back Frank Gore said he hopes to receive a contract extension before the season opener. On Aug. 2, when Gore arrived at training camp after a four-day holdout, Jim Harbaugh said the team anticipated working out a deal “sooner rather than later.”

“Hopefully it will get done before the season,” Gore said. “If it doesn’t, I’ve just got to go play and if I have to be a free agent, I’ll be a free agent.”